(a) Field of the invention
The present invention relates to a magnetic sensor and more particularly, it relates to a magnetic sensor for detecting rotation information such as the rotating speed and the position of a rotating body with the use of magnetoresistance effect elements.
(b) Prior Art
Rotary encoders with the output of digital quantity sensors which detect rotating positions or rotating speed of rotating bodies such as drums or discs are in demand, especially among these encoders, magnetic encoders utilizing magnetoresistance effect elements which have high sensitivity, excellent frequency characteristics, and simple construction are considered to have a bright future as magnetic sensors.
The magnetic sensor utilizing the magnetoresistance effect elements comprises eight magnetoresistance effect elements which are formed into strips and disposed in parallel to each other on a substrate made of glass or the like, wherein each group consisting of four elements forms a bridge circuit. When the magnetic sensor thus constituted is arranged in close proximity to a rotating body, for example, a rotating surface of a drum on which magnetic signals are recorded, the electric resistance of magnetoresistance effect elements of the magnetic sensor is changed according to the change of the magnetic field caused by the rotating body, so that rotation information signals based on the change of the electric resistance can be obtained from abovementioned bridge circuits.
As described above, eight strip-shaped magnetoresistance effect elements arranged in parallel to each other constitute the magnetic sensor, and these elements are formed, for example, as shown in FIG. 3 (a) in a method wherein an element layer 2 is formed with a film of a ferromagnetic substance such as Permalloy on a substrate 1 to constitute magnetoresistance effect elements and after that as shown in FIG. 2 (b) eight pieces of magnetoresistance effect elements 3 are formed in strip shapes on the substrate 1 by photo-etching.
When eight pieces of magnetoresistance effect elements are formed in parallel to each other on the substrate 1 by etching, both sides of these eight pieces of magnetoresistance effect elements are left as wide spaces and etching solution is collected in these areas. The collected solution affects the magnetoresistance effect elements on both sides, and the width of the magnetoresistance effect elements on both sides are formed thinner than other elements. Consequently, resistance values of the magnetoresistance effect elements on both sides are made to be higher than those of other elements. It prevents the forming of the magnetoresistance effect elements with uniform resistance values and so it is necessary to adjust the resistance values of these elements on both sides with the use of a variable resistor etc. Such additional adjustment work is uneconomical requiring longer time for adjustment and also troublesome.